metamorphic

Biotite-rich gneiss (probable)

Foliated quartz–feldspar–mica gneiss; composition typically quartz (SiO₂), feldspars, and biotite mica

AI-generated identification · may be incorrect

Dark gray, coarse-grained, weakly to moderately foliated, with sparkling mica and pale granular minerals. Quartz and feldspar are Mohs 6–7; biotite is about 2.5–3, with mica cleavage; generally vitreous to pearly luster and no obvious crystal faces.

Identified September 12, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed by high-grade metamorphism of granite or other felsic protoliths, commonly during mountain building. The specimen is likely Paleozoic or older in the Alpine region, but age cannot be determined from the photograph.

Uses & applications

Used locally as crushed stone, aggregate, building stone, and decorative material; attractive pieces may be collected, though this example appears ordinary.

Geological facts

The alternating or streaky mica-rich texture records directed pressure and recrystallization. Nearby southeastern Swiss Alpine geology makes metamorphic gneiss a plausible identification.

Field identification & locations

Look for planar mica alignment, quartz/feldspar grains, and a hard, nonporous texture; it should scratch glass but mica flakes can peel. Distinguishing it from granite requires visible foliation; a close photograph or fresh broken surface would help.